In the metallurgical industry there is a need to know, as accurately as possible, the composition of the material that has been mined as sand, or mined as rock and then crushed to granular form, and which constitutes the feedstock for a processing plant.
The main reason why this information relating to composition is of vital importance is that the way in which the various operating parameters of the minerals processing plant have to be set depends on the proportions of the constituents in the feedstock. These proportions vary continually as mining progresses through the body of ore being mined, and adjustments thus have to be made to ensure that the plant is being run at maximum efficiency to achieve the best possible yield.
Another reason why this information is of importance is that changes occur in environmental variables such as humidity and temperature, as well as in equipment variables such as supply voltage and the physical condition of the processing plant. Any of these variables may cause certain stages of the process to produce less than optimum intermediate streams of minerals. Ideally these error conditions have to be detected and corrected as soon as possible. Therefore, up-to-date ie. so-called “real time” information on the composition of the mineral being processed is required to ensure that the plant is being run at maximum benefication yield.
The information required for these purposes is obtained by analysing the mineral being processed at various stages of its treatment. The proportions of the constituents as the mineral passes through the processing plant can be used as an indication of the efficiency of the plant and enable adjustments to the process to be made to achieve maximum benefication yield.
Because of a lack of accurate, up-to-date knowledge on the composition of the mineral, and the fear that valuables may be dumped with the discard, plant operators adopt a conservative approach and recycle a proportion of the mineral emerging from some or all of the stages to ensure that the least possible amount of valuables is lost. If accurate real time knowledge on the composition of the mineral beneficated is available, recycling can be reduced without loss of valuable products.
The known methods of determining the proportions of the constituents in the minerals undergoing processing can be divided into “human” and “machine”. The main “human” method involves the preparation of a sample, the proportions of the constituents of which are the same as the proportions in the mineral being processed. Obtaining the sample is a lengthy procedure. The first step is to take a number of kilograms of the granular mineral to ensure that the constituents of the sample are as representative as possible of the constituents of the bulk. The sample is split into small portions and then some of these portions recombined until the procedure has eliminated any remaining difference between the proportions in the sample and the proportions in the mineral being processed. The grains in the sample are then identified and counted by a skilled grain counter using a microscope and an optical grid over which the grains are spread.
Another “human” method relies on the skill of the person carrying out the test as it is based on the difference between the colour of the sample being checked and the colour of a standard sample. This is not a particularly accurate method as the human eye cannot pick up small changes in contrast or colour.
The “machine” methods are numerous but these have a number of shortcomings. Some require expensive equipment and, generally, sample preparation is time consuming. Also, some of the equipment is such that it can only be run by trained scientists and even then only in laboratory conditions. Examples of “machine” methods known to the Applicant as at 23 Jan. 2002, as well as a recent development in the spectral analysis of material in particulate form, are described in WO 03/062804.
The present invention seeks to provide a new analysis method and new analysis apparatus which enable real time information on the composition of a material to be obtained.
The method and apparatus of the present invention are primarily intended for use in the processing of minerals but can be used in other industries where the composition of a material must be determined.